The invention generally relates to a method for evacuating a turbine condenser, particularly during a starting operation. The invention also generally relates to a device for carrying out the method.
During the operation of a steam turbine installation, the steam, which is generally produced in a steam generator and expanded in a steam turbine to produce work, is condensed in a condenser connected downstream of the steam turbines. The condensate which appears in the turbine condenser is returned to the water/steam circuit of the steam turbine. In order to extract air contained in the turbine condenser or main condenser during the operation of the turbine installation, so-called operational jet pumps are frequently employed. These are joined to a propellant steam main and are connected to an auxiliary condenser connected downstream of the main condenser. Air mains connected to the main condenser are joined to the suction side of the operational jet pumps, which operate on the jet pump principle.
During the starting or restarting of the steam turbine, it is necessary to first evacuate the turbine condenser or main condenser. During this operation, the turbine condenser, and therefore the steam turbine installation, is evacuated from 1.0 bar down to approximately 0.3 bar within, for example, half an hour, by way of a so-called starting steam ejector, to which propellant steam is in turn admitted according to the jet pump principle. The steam/air mixture leaving the pressure side of the starting jet pump is conveyed to the open air via a pipeline. In this arrangement, the pipeline must be designed for the mixed temperature which occurs in the steam/air mixture and it is to be equipped with a noise suppressor because of environmental requirements which have to be met.
A disadvantage of this arrangement is that the propellant steam, which is usually extracted from the water/steam circuit of the steam turbines, is lost so that the feed water circuit of the turbine condenser has to be topped up by a corresponding quantity of feed water. This loss of feed water increases with increasing number of starting procedures and involves additional costs for the feed water treatment necessary.
An embodiment of the invention provides a method for evacuating a turbine condenser, in particular during the starting operation, by way of which the disadvantages mentioned are avoided in a particularly simple manner. In addition, a device which is for carrying out the method is provided.
With respect to the method, air contained in a turbine condenser may be extracted by way of propellant steam, conducted via a starting jet pump, and this air, together with the propellant steam. The extracted air is conducted into an auxiliary condenser connected downstream of the turbine condenser. Therefore, the propellant steam conducted via the starting jet pump is together with the air extracted from the turbine condenser introduced into the auxiliary condenser.
By this manner, the propellant steam condensing in the auxiliary condenser may be again supplied as condensate to the feed water circuit of the turbine condenser and, therefore, to the steam turbine installation. The air contained in the propellant steam is expediently removed from the auxiliary condenser.
In order to additionally permit a starting operation lasting several hours, at least half of the condensate quantity or feed water quantity corresponding to the nominal operation may be expediently made available for cooling in the auxiliary condenser. This only requires a corresponding design of a control valve which adjusts, in the usual manner, the condensate flow from the main condenser which is conducted via the auxiliary condenser.
In order, furthermore, to keep the heating of the condensate flow conducted via the auxiliary condenser within necessary limits, a major part, approximately 75% for example, of the condensate flow conducted by way of a condensate pump via the auxiliary condenser may be conducted via the condenser tubes of the main condenser. By this manner, the cooling water cooling of the main condenser is used to recool the partial condensate flow conducted via the auxiliary condenser. The relatively small proportion, approximately 25%, of the condensate flow, i.e. of the condensate quantity conveyed per unit time, is therefore available for the cooling, which is also necessary during the starting operation, of the quantities of water removed from the steam turbine.
With respect to the device, a starting jet pump is provided, which is connected to a propellant steam main and to an auxiliary condenser at the pressure end and is connected to the air main connected at the suction end to the main condenser.
The advantages achieved by way of the invention include, but are not limited to, the following. The propellant steam extracted from the water/steam circuit of a steam turbine, and employed for evacuating a turbine condenser, may be resupplied to the circuit by way of its introduction into the auxiliary condenser of a steam turbine installation. This avoids an undesirable topping up of feed water in the circuit. Furthermore, there is an additional saving with respect to a previously usual noise suppressor in the steam jet, air and pump system for removal of air from the turbine and condensate.